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Always add a .note.GNU-stack section if -r. 

With this patch, lld creates a .note.GNU_stack and adds that to an
output file if it is creating a re-linkable object file (i.e. if -r
is given). If we don't do this, and if you use GNU linkers as a final
linker, they create an executable whose stack area is executable,
which is considered pretty bad these days.

Differential Revision: https://reviews.llvm.org/D51400

llvm-svn: 340902
This commit is contained in:
Rui Ueyama 2018-08-29 07:27:09 +00:00
parent 398f81b3b4
commit 025bb56a86
8 changed files with 47 additions and 16 deletions
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9
lld/ELF/SyntheticSections.h
View File

@ -135,6 +135,15 @@ protected:
uint64_t Size = 0;
};
// .note.GNU-stack section.
class GnuStackSection : public SyntheticSection {
public:
GnuStackSection()
: SyntheticSection(0, llvm::ELF::SHT_PROGBITS, 1, ".note.GNU-stack") {}
void writeTo(uint8_t *Buf) override {}
size_t getSize() const override { return 0; }
};
// .note.gnu.build-id section.
class BuildIdSection : public SyntheticSection {
// First 16 bytes are a header.

8
lld/ELF/Writer.cpp
View File

@ -399,6 +399,14 @@ template <class ELFT> static void createSyntheticSections() {
InX::Iplt = make<PltSection>(true);
Add(InX::Iplt);
// .note.GNU-stack is always added when we are creating a re-linkable
// object file. Other linkers are using the presence of this marker
// section to control the executable-ness of the stack area, but that
// is irrelevant these days. Stack area should always be non-executable
// by default. So we emit this section unconditionally.
if (Config->Relocatable)
Add(make<GnuStackSection>());
if (!Config->Relocatable) {
if (Config->EhFrameHdr) {
InX::EhFrameHdr = make<EhFrameHeader>();

2
lld/test/ELF/relocatable-bss.s
View File

@ -20,7 +20,7 @@
# CHECK-NEXT: Version:
# CHECK-NEXT: Entry:
# CHECK-NEXT: ProgramHeaderOffset:
# CHECK-NEXT: SectionHeaderOffset: 0xD8
# CHECK-NEXT: SectionHeaderOffset: 0xE8
# CHECK-NEXT: Flags [
# CHECK-NEXT: ]
# CHECK-NEXT: HeaderSize:

4
lld/test/ELF/relocatable-comdat-multiple.s
View File

@ -8,7 +8,7 @@
# CHECK-NEXT: Group {
# CHECK-NEXT: Name: .group
# CHECK-NEXT: Index: 2
# CHECK-NEXT: Link: 8
# CHECK-NEXT: Link: 9
# CHECK-NEXT: Info: 1
# CHECK-NEXT: Type: COMDAT
# CHECK-NEXT: Signature: aaa
@ -20,7 +20,7 @@
# CHECK-NEXT: Group {
# CHECK-NEXT: Name: .group
# CHECK-NEXT: Index: 5
# CHECK-NEXT: Link: 8
# CHECK-NEXT: Link: 9
# CHECK-NEXT: Info: 6
# CHECK-NEXT: Type: COMDAT
# CHECK-NEXT: Signature: bbb

2
lld/test/ELF/relocatable-comdat.s
View File

@ -30,7 +30,7 @@
# CHECK-NEXT: Group {
# CHECK-NEXT: Name: .group
# CHECK-NEXT: Index: 2
# CHECK-NEXT: Link: 5
# CHECK-NEXT: Link: 6
# CHECK-NEXT: Info: 1
# CHECK-NEXT: Type: COMDAT
# CHECK-NEXT: Signature: abc

4
lld/test/ELF/relocatable-comdat2.s
View File

@ -13,7 +13,7 @@
# CHECK-NEXT: Group {
# CHECK-NEXT: Name: .group
# CHECK-NEXT: Index: 2
# CHECK-NEXT: Link: 7
# CHECK-NEXT: Link: 8
# CHECK-NEXT: Info: 1
# CHECK-NEXT: Type: COMDAT
# CHECK-NEXT: Signature: bar
@ -24,7 +24,7 @@
# CHECK-NEXT: Group {
# CHECK-NEXT: Name: .group
# CHECK-NEXT: Index: 4
# CHECK-NEXT: Link: 7
# CHECK-NEXT: Link: 8
# CHECK-NEXT: Info: 2
# CHECK-NEXT: Type: COMDAT
# CHECK-NEXT: Signature: zed

18
lld/test/ELF/relocatable-many-sections.s
View File

@ -9,8 +9,8 @@
## sections amount is greater than SHN_LORESERVE.
# RUN: llvm-readobj -file-headers %t | FileCheck %s --check-prefix=HDR
# HDR: ElfHeader {
# HDR: SectionHeaderCount: 0 (65543)
# HDR-NEXT: StringTableSectionIndex: 65535 (65541)
# HDR: SectionHeaderCount: 0 (65544)
# HDR-NEXT: StringTableSectionIndex: 65535 (65542)
## Check that:
## 1) 65541 is the index of .shstrtab section.
@ -18,13 +18,15 @@
## 3) .symtab_shndxr entry size and alignment == 4.
## 4) .symtab_shndxr has size equal to
## (sizeof(.symtab) / entsize(.symtab)) * entsize(.symtab_shndxr) = 0x4 * 0x180048 / 0x18 == 0x04000c
# RUN: llvm-readelf -sections -symbols %t | FileCheck %s
## [Nr] Name Type Address Off Size ES Flg Lk Inf Al
# CHECK: [65538] .bar
# CHECK-NEXT: [65539] .symtab SYMTAB 0000000000000000 000040 180078 18 65542 65539 8
# CHECK-NEXT: [65540] .symtab_shndxr SYMTAB SECTION INDICES 0000000000000000 1800b8 040014 04 65539 0 4
# CHECK-NEXT: [65541] .shstrtab STRTAB 0000000000000000 1c00cc 0f0035 00 0 0 1
# CHECK-NEXT: [65542] .strtab STRTAB 0000000000000000 2b0101 00000c 00
# [Nr] Name Type Address Off Size ES Flg Lk Inf Al
# CHECK: [65539] .note.GNU-stack PROGBITS 0000000000000000 000040 000000 00 0 0 1
# CHECK: [65540] .symtab SYMTAB 0000000000000000 000040 180078 18 65543 65539 8
# CHECK: [65541] .symtab_shndxr SYMTAB SECTION INDICES 0000000000000000 1800b8 040014 04 65540 0 4
# CHECK: [65542] .shstrtab STRTAB 0000000000000000 1c00cc 0f0045 00 0 0 1
# CHECK: [65543] .strtab STRTAB 0000000000000000 2b0111 00000c 00 0 0 1
# 5) Check we are able to represent symbol foo with section (.bar) index > 0xFF00 (SHN_LORESERVE).
# CHECK: GLOBAL DEFAULT 65538 foo

16
lld/test/ELF/relocatable.s
View File

@ -4,6 +4,7 @@
# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %p/Inputs/relocatable2.s -o %t3.o
# RUN: ld.lld -r %t1.o %t2.o %t3.o -o %t
# RUN: llvm-readobj -file-headers -sections -program-headers -symbols -r %t | FileCheck %s
# RUN: llvm-objdump -section-headers %t | FileCheck -check-prefix=SECTION %s
# RUN: llvm-objdump -s -d %t | FileCheck -check-prefix=CHECKTEXT %s
## Test --relocatable alias
@ -37,8 +38,8 @@
# CHECK-NEXT: ProgramHeaderEntrySize: 0
# CHECK-NEXT: ProgramHeaderCount: 0
# CHECK-NEXT: SectionHeaderEntrySize: 64
# CHECK-NEXT: SectionHeaderCount: 7
# CHECK-NEXT: StringTableSectionIndex: 5
# CHECK-NEXT: SectionHeaderCount: 8
# CHECK-NEXT: StringTableSectionIndex: 6
# CHECK-NEXT: }
# CHECK: Relocations [
@ -51,6 +52,17 @@
# CHECK-NEXT: 0x4E R_X86_64_32S yyy 0x0
# CHECK-NEXT: }
# SECTION: Sections:
# SECTION: Idx Name Size Address Type
# SECTION: 0 00000000 0000000000000000
# SECTION: 1 .text 00000056 0000000000000000 TEXT
# SECTION: 2 .rela.text 00000090 0000000000000000
# SECTION: 3 .bss 00000018 0000000000000000 BSS
# SECTION: 4 .note.GNU-stack 00000000 0000000000000000
# SECTION: 5 .symtab 00000168 0000000000000000
# SECTION: 6 .shstrtab 00000041 0000000000000000
# SECTION: 7 .strtab 0000002d 0000000000000000
# CHECKTEXT: Disassembly of section .text:
# CHECKTEXT-NEXT: main:
# CHECKTEXT-NEXT: 0: c7 04 25 00 00 00 00 05 00 00 00 movl $5, 0